The present invention relates generally to the art of sputtering metal-containing films on non-metallic substrates, and more particularly to the art of magnetic sputtering of multiple-layer metal/dielectric transparent films on glass.
U.S. Pat. No. 3,990,784 to Gelber discloses a coated architectural glass system comprising a transparent substrate and a multi-layer coating comprising first and second metal layers with a dielectric layer between them, wherein the first and second metal layers have a thickness ratio so that the transmission of the coating can be changed independent of its reflection properties by varying the thickness of the metal layer while maintaining the ratio constant. The dielectric has a thickness such that the reflection from the coating is not strongly colored.
U.S. Pat. No. 4,022,947 to Grubb et al discloses a transparent panel capable of transmitting a desired portion of visible radiation while reflecting a large portion of incident solar radiation and a method of preparing same, by sputtering an iron, nickel and chromium alloy to obtain a transparent metal film, and reactively sputtering the same or a similar alloy in the presence of oxygen to form an oxide film. In one preferred embodiment, the metal film lies between the substrate and the metal oxide film. In another preferred embodiment, the metal oxide film lies between the substrate and the metal film.
U.S. Pat. No. 4,534,841 to Hartig et al discloses solar-control glazing produced by applying first an oxide layer having an optical thickness of 20 to 280 nanometers to a transparent substrate by cathodic evaporation in an oxygen-containing atmosphere, and second a chromium nitride layer having a geometric thickness of 10 to 40 nanometers applied in an atmosphere consisting of an inert gas, such as argon, and nitrogen. An optical third dielectric layer may be applied to the second layer. The oxide layer is selected from oxides of tin, titanium and aluminum.
Architectural glass products with metallic and/or metal oxide films are growing in importance as energy demands for heating and cooling become increasingly expensive. Coated glass architectural products generally fall into two categories, solar energy control and high transmittance, low emissivity coated products.
Solar energy control glass products are generally glass substrates, often tinted, coated with a low visible transmittance colored film which reduces solar energy transmittance through the windows into the building interior, thereby reducing air conditioning costs. These products are most effective in warm climates and are most often seen in commercial construction. In areas where heating costs are of greater concern, and particularly in residential construction, high transmittance, low emissivity coatings are desirable in order to allow high transmittance of visible light into the interior while reflecting infrared radiation to retain heat inside the building. High transmittance, low emissivity coatings are typically multiple layer films wherein an infrared reflecting metal such as silver, gold or copper is sandwiched between anti-reflective metal oxide layers such as bismuth, indium and/or tin oxides. Solar energy control films, on the other hand, are typically single layer films of one or more metals or oxides of metals such as cobalt, iron, chromium, nickel, copper, etc.
The simplest method of producing a colored reflective coating is to use the body color of the metal. Thus, depositing copper produces a copper colored coating, gold produces a gold color, nickel a gray color, and so on. A more sophisticated coating technique is to modify the metal color or create a new color by introducing an absorption-colored coating in front of the metal. The interference effect is usually weak, but if reasonably large and equal reflections are made to interfere, the effect can be quite strong. This can be done by using dielectrics of high refractive index, or by enhancing the reflectance of the dielectric layer with metal layers. This involves using the two-layer sequence of metal oxide dielectric/metal or the three layer sequence of metal/metal oxide dielectric/metal.
Early well known films were of the body color variety. Wet chemical methods for producing such films for solar energy control are well known from U.S. Pat. Nos. 3,846,152; 4,091,172; 3,723,158; and 3,457,138. When vacuum coating technologies became commercially available, those existing colored coatings could be duplicated using essentially the same metals as the originals. Sputtering technologies for producing metallic solar energy control films are disclosed in U.S. Pat. Nos. 4,512,863 and 4,594,137. Disadvantages of metallic coatings are their lack of color variety and intensity, and the large number of materials and target sequences needed to make them. A desirable new series of coatings should provide a maximum number of colors from a minimum number of materials. For this to be accomplished, the interference color type of coating is ideal since its color can be changed by changing the thickness of the dielectric layer, and its transmittance and reflectance by changing the thickness of the metal layer or layers. The other desirable properties of a new series of coatings are intense saturated color, low reflectance, and second surface monolithic durability; i.e., the coating should be hard and chemically durable. In addition, the materials used should be inexpensive, non-toxic, and fast-sputtering. The reflectance color of a material is described by its luminous reflectance spectrophotometric curve. The intense colors are produced by large amplitudes of the curve, and low reflectance requires the curve minimum to approach zero. Second order interference colors are more intense than first order, but third order interference colors become less intense. In general, high refractive index materials produce high reflectances or large curve amplitudes. High refractive index dielectric materials also give a more intense color for double layer coating. For a metal/dielectric/metal sequence of layers, it appears that a lower refractive index dielectric material may give acceptable results.